1. Field of the Invention
This application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2004-88999 filed in Japan on Mar. 25, 2004, the entire contents of which are hereby incorporated by reference.
The present invention relates to tamper switch structures used for security sensors such as passive infrared sensors (PIR sensors) and active infrared sensors (AIR sensors), and to security sensors including such tamper switch structures. In particular, the invention relates to measures for adding a tampering detection function to security sensors of outdoor installation type (the type installed at locations where water such as rainwater pours over) with a simple configuration.
2. Description of the Related Art
Conventionally, the PIR sensor, which is one type of security sensors, contains a PIR element, and is so configured that this PIR element detects an intruder from the difference between the temperature of the intruder's body and the ambient temperature by receiving infrared radiation from the human body within a detection area.
On the other hand, in an attempt to illegally intrude into a room in which this type of sensor is installed, the sensor body may be removed from the mounting plate in non-alert operation, and be mounted on the mounting plate again after the sensor is rendered unable to detect a human body by corrupting it (tampering) such as attaching paper tape or plastic tape or spraying transparent paint that does not transmit infrared radiation onto the incident path of infrared radiation to the PIR element within the sensor body. In this case, the sensor will not be able to detect illegal intruders in alert operation. Also, the sensor body may be removed from the mounting plate in non-alert operation and stolen, so that the detection of illegal intruders is disabled.
Therefore, intruder detection systems having this type of sensor include a tampering detection function that operates also in non-alert operation, and are configured so as to output a tampering detection signal (hereinafter, referred to as “trouble signal”) when the sensor body is removed from the mounting plate.
In the case of providing such a tampering detection function, it is necessary to provide a large number of wiring, namely, power supply wiring, transmission wiring for a human body detection signal for sending a detection signal at the time of detecting a human body and wiring for tampering detection, between the mounting plate on which the sensor body is mounted and a control panel that is placed at a different location, resulting in a poor operability of the intruder detection systems.
In view of that the power supply wiring is disconnected when the above-described stealing is carried out, it is conceivable, as one measure to solve this problem, to adopt a configuration that allows the detection of disconnection of the power supply wiring, thereby making it possible to detect the stealing, without requiring the wiring for tampering detection.
Conventional security sensors such as the PIR sensor have required relatively large power consumption, and thus have required the above-described power supply wiring. However, in recent years, the development of sensing elements such as the PIR element has advanced to reduce the power consumption significantly, making it possible to drive the security sensors with their internal batteries for a long period of time, without requiring power supply from the power supply wiring.
The fact that the power supply wiring becomes unnecessary in this way can lead to that it is impossible to realize the above-described configuration, such as that “allows the detection of disconnection of the power supply wiring, thereby making it possible to detect the stealing”. In other words, as the power supply wiring has become unused due to the development of sensing elements, it has become necessary to realize a configuration in which the sensor body includes the tampering detection function.
In order to realize this, JP H5-54269A (hereinafter, referred to as Patent reference 1) discloses that an opening is formed on the rear surface of a sensor casing, and that the actuating piece of a tamper switch housed inside the sensor is projected outside from the opening. That is, in a state in which the sensor is normally mounted on a wall surface, the actuating piece is depressed by the wall surface and no trouble signal is transmitted. When the sensor has been removed from the wall surface or when the sensor body has been removed from the mounting plate, the depressing of the actuating piece is released, and as a result, the trouble signal is transmitted.
As described above, although the type of security sensors to which the power supply wiring is connected can detect the above-described stealing by allowing the detection of disconnection of the power supply wiring, they cannot detect the tampering such as attaching paper tape or plastic tape or spraying transparent paint that does not transmit infrared radiation onto the incident path of infrared radiation without disconnecting the power supply wiring. Therefore, it is preferable that the sensor body includes the tampering detection function not only in wireless security sensors, which require no power supply wiring, but also in security sensors of the type to which the power supply wiring is connected (wired security sensors).
The security sensor including the tamper switch, disclosed in Patent reference 1 above, has been proposed for the indoor installation type. This is evident from the fact that no consideration is given at all to waterproof for the opening from which the actuating piece of the above-described tamper switch is projected.
Therefore, in the case of using this type of security sensor as the outdoor installation type, the tamper switch structure disclosed in Patent reference 1 above cannot be used as it is. The reason is that, since rainwater or the like may poured over security sensors installed outdoor, rainwater or the like may enter the structure disclosed in Patent reference 1 above from the opening provided for projecting the actuating piece of the tamper switch, causing a failure of the sensor.
The present invention has been made in view of the above-described problems, and it is an object thereof to provide a tamper switch structure for providing a sensor body with a tampering detection function that can provide an excellent tampering detection function while reliably preventing a flood from outside, and a security sensor including such a tamper switch structure.